Circuit modules, whether of the single in-line package (SIP) or the dual in-line package (DIP), have typically been of two basic types of construction.
One of the basic types of construction has utilized a thin ceramic substrate upon which an electronic circuit is deposited or attached; and then the substrate with the electronic circuit is encapsulated in a housing. The electronic circuit generally contains thick film and or chip devices, such as resistors and capacitors connected with thick film conductors. A common method of forming the housing has been to mold a thermoset plastic over the substrate. Another method of encapsulating has included using two cover portions and then injecting a potting compound between the cover portions as taught by Fox et al. in U.S. Pat. No. 4,012,579. In a similar method, a single cover has been adhesively secured over the substrate and the electrical circuit by use of an adhesive tape as taught by Riley in U.S. Pat. No. 3,939,558.
However, with the advent and increasing use of smaller circuit modules, slightly less than 4 mm. thick or which can be only 2 mm. thick, encapsulated designs have had two serious disadvantages. One of these disadvantages has been relatively weak and insecure attachment of the connector pins both to the housing and to the electrical circuit, thus severely limiting the reliability of the circuit module. The other serious disadvantage has been poor heat dissipation properties and a resultant poor power rating for the molded and potted constructions.
Both the problem of the weak mechanical and electrical attachment of the connector pins and the problem of poor heat dissipation have been solved by constructions taught by Brady et al. in U.S. Pat. No. 3,280,378, and by Brady in U.S. Pat. No. 3,346,774, both of common assignee. In these designs, a thick ceramic substrate having dimensions almost the same as the housing is used, the connector pins are securely attached to the substrate by force fitting the pins into holes or recesses provided in the substrate, the connector pins are electrically connected to the electrical circuit by soldering, and the electrical circuit is preferably insulated with a nonconductive coating. The resulting module is both mechanically and electrically superior. In addition, the heat dissipation properties of the module are superior and the power rating can be higher because a ceramic substrate has heat conductivity properties that are approximately sixty times as great as a thermosetting plastic used for encapsulating a thin substrate. Also the heat dissipation properties are superior even when the electrical circuit on the thick ceramic substrate is covered by a thin layer of nonconductive material because more than 90% of the volume of the housing defining the module used in the design is ceramic which has excellent heat conductivity.
Circuit modules of the type described above, using a thick ceramic substrate, using a circuit that includes thick film conductors and resistors, and using a thin nonconductive coating, have had one limitation. This limitation has been the inability to attach a separate electrical device, such as a chip capacitor, to the circuit without an excessive increase in the thickness of the circuit module. This disavantage becomes more severe when the circuit requires the attachment of a capacitor that is almost 1 mm. thick.
The present invention eliminates this one disadvantage of the construction which is taught in U.S. Pat. Nos. 3,280,378 and 3,346,774, while retaining all of the advantages thereof.